- Code blocks nested inside of lists won't be checked
for line starts
- The minimal indentation to continue a multi-paragraph list
has been reduced to 1 space, instead of 4. This is not what the standard
says, but what the Markdown.PL does.

If the first header of a document is a level three header the first list
is nested two times. To prevent this an offset if set when the first
header is found and after that the level is changed to (level - offset).